基于反演设计的机械臂非奇异终端神经滑模控制

针对具有建模误差和不确定干扰的多关节机械臂的轨迹跟踪问题,设计反演非奇异终端神经滑模控制。该方案是采用能有限时间收敛的非奇异终端滑模面,根据滑模控制原理和反演方法设计反演滑模控制器;对于反演滑模控制系统中由于建模误差和不确定干扰造成的不确定因素的上界,设计径向基(Radial basis function, RBF)神经网络自适应律,在线估计不确定因素的上界;利用李亚普诺夫定理证明了系统的稳定性。仿真结果表明,该方法具有良好的轨迹跟踪性能,提高对于建模误差和不确定干扰等因素的鲁棒性,削弱了抖动。     

Backstepping-based Decentralized PID Controller Design for MIMO Processes

A novel decentralized PID controller design procedure based on backstepping principles is presented to operate multiple-input multiple-output(MIMO)dynamic processes.The first key feature of the design procedure is that a whole MIMO control system is decomposed into multiple control loops,therefore the sub-controllers can be efficiently flexibly designed in parallel prototype. The second key feature is that the decentralized controller has equivalency to those designed by backstepping approach.As a complementary support to the design procedure,the sufficient condition of the whole closed-loop system stability is analyzed via the small gain theorem and it can be proven that the process tracking performance is improved.The simulation results of the Shell benchmark control problem are provided to verify the effectiveness and practicality of the proposed decentralized PID control.     

H∞ control for a class of structured time-delay systems

In this paper, we design an H_∞ controller for a class of lower-triangular time-delay systems. Backstepping is applied to construct an explicit feedback controller, and the closed-loop system maintains internal stability and an L₂-gain from the disturbance input to the output. The design is delay-dependent. Simulations on an example system demonstrate the good performance of the proposed design.     

Robust adaptive output stabilization using dynamic normalizing signal

For a class of nonlinear systems with dynamic uncertainties, robust adaptive stabilization problem is considered in this paper. Firstly, by introducing an observer, an augmented system is obtained. Based on the system, we construct an exp-ISpS Lyapunov function for the unmodeled dynamics, prove that the unmodeled dynamics is exp-ISpS, and then obtain a dynamic normalizing signal to counteract the dynamic disturbances. By the backstepping technique, an adaptive controller is given, it is proved that all the signals in the adaptive control system are globally uniformly ultimately bounded, and the output can be regulated to the origin with any prescribed accuracy. A simulation example further demonstrates the efficiency of the control scheme.     

Robust formation control without velocity measurement of the leader robot

In this paper a control problem of leader–follower motion coordination of multiple nonholonomic mobile robots is addressed and subsequently in the proposed scheme, a reference trajectory generated based on the information from the leader is tracked by the follower robots. To alleviate demanded information on the leader, specifically to eliminate the measurement requirement or estimation of the leader's velocity and dynamics, a virtual vehicle is constructed whereby its trajectory converges to the reference trajectory of the follower. Trajectory tracking controller is then designed to allow the follower robot to track the virtual vehicle using neural network approximation, in combination with the backstepping and Lyapunov direct design technique and finally the performance and effectiveness of the controller is verified throughout the experiments.     

不确定非线性系统的非光滑控制及应用

针对一类具有严格反馈结构形式的不确定非线性系统,研究非光滑鲁棒控制问题。在一定的假设条件下,基于backstepping设计方法,设计鲁棒非光滑控制律,证明闭环系统的鲁棒稳定性。将所得结果应用于飞行器的末制导问题,设计非光滑末制导律,并进行数值仿真研究。仿真结果说明了方法的有效性。     

Barrier Lyapunov functions for the output tracking control of constrained nonlinear switched systems

In this paper, we investigate the output tracking control problem of constrained nonlinear switched systems in lower triangular form. First, when all the states are subjected to constraints, we employ a Barrier Lyapunov Function (BLF), which grows to infinity whenever its arguments approach some finite limits, to prevent the states from violating the constraints. Based on the simultaneous domination assumption, we design a continuous feedback controller for the switched system, which guarantees that asymptotic output tracking is achieved without transgression of the constraints and all closed-loop signals remain bounded, provided that the initial states are feasible. Then, we further consider the case of asymmetric time-varying output constraints by constructing an appropriate BLF. Finally, the effectiveness of the proposed results is demonstrated with a numerical example.     

带有时滞的未知非仿射非线性系统自适应模糊跟踪控制

应用自适应模糊逼近方法研究了一类带有时滞的未知非仿射非线性系统的跟踪控制问题.系统的实际控制器是按照Backstepping设计过程经逐步反推而得到, 在每一步设计中需要用自适应模糊逻辑系统来逼近未知的非线性函数.为了降低控制设计对先验知识的依赖性, 取消须事先已知模糊基函数的限制, 采用非线性参数化的模糊逻辑系统作为逼近器.由于逼近器中的未知参数彼此之间呈非线性关系, 无法直接得到在线估计这些参数的自适应律.为了实现对相关参数的在线调节, 先应用Taylor展开式将呈非线性关系的参数分离, 使其相互之间具有线性关系, 然后再基于Lyapunov第2方法给出相应参数的自适应调节律.最后, 通过一个仿真实例来验证所给方法的有效性.结果表明:所得自适应模糊控制器能有效补偿时滞的影响, 保证闭环系统中所有信号均有界, 而且输出跟踪误差能收敛到原点的任意小邻域内.     

基于反步控制的非线性干扰观测器的外部不确定干扰的电液位置伺服系统

由于电液系统中存在各种非线性因素以及不确定干扰,为提高电液位置伺服系统在干扰下的控制精度,以电液振动台为控制对象,建立非线性模型,利用干扰观测器对干扰力进行观测,并通过反步控制器进行削弱和补偿,利用李雅普诺夫理论保证闭环系统的全局稳定.对设计的控制器进行仿真和实验,模拟在有外界未知干扰力下的位置控制,实现对干扰的抑制.实验表明:该控制策略能够很好的提高电液位置伺服系统的跟踪性能.     

Design, analysis and experimental validation of a robust nonlinear path following controller for marine surface vessels

The problem of path following for marine surface vessels using the rudder angle is addressed in this paper. A four-degree-of-freedom nonlinear surface vessel model, together with the Serret-Frenet equations, is introduced to describe the ship dynamics and path following error dynamics. While similar models have been used and reported in the literature for path following control algorithm development, the novelty of the approach presented in this work lies in the following aspects. (a) The back-stepping nonlinear controller design is based on feedback dominance, instead of feedback linearization and nonlinearity cancelation; (b) additional design parameters are employed in the Lyapunov function that lead to simplification of the controller in the design procedure and normalization of different variables in the Lyapunov function to improve the controller performance; (c) relying on feedback dominance and the introduction of the additional parameters in the Lyapunov function, the resulting controller is almost linear, with very benign nonlinearities allowing for analysis and evaluation; and (d) the performance of the nonlinear controller, in terms of path following, is analyzed for robustness in the presence of model uncertainties. The simulation results are presented to verify and illustrate the analytic development and the effectiveness of the resulting control against rudder saturation and rate limits, and delays in the control execution, as well as measurement noises. Furthermore, the control design is validated by experimental results conducted in a tank using a model ship.